A fluid-passage change-over mechanism, such as shown in FIG. 1, was heretofore used in handling a powdery or granular material. In FIG. 1. a main pipe 2 is connected to the inlet side (the left side in the figure) of a change-over mechanism 1 of a Y type and two circuit pipes 3 and 4 are, respectively, connected to the outlet side (the right side in the figure) of the change-over mechanism 1. Change-over mechanism 1 of such type as referred to above was manufactured and sold with the cross section thereof formed in a square hollow shape for reasons of function and machining. A change-over valve 5 of a square shape is provided within a pipe with the section thereof formed as a square and hollow shape and is combined with a driving arm 7 of a driving mechanism, such as an air cylinder 6, which is provided outside change-over mechanism 1. Change-over valve 5 swings around a pivot 8 by an actuation of air cylinder 6 to change-over the powdery or granular material which is transferred from main pipe 2 to circuit pipe 3 or 4.
In the example stated above, since main pipe 2 with the section thereof formed as a circular shape must be connected to change-over mechanism 1 with the section thereof formed in a square hollow shape at the inlet side of change-over mechanism 1 and circuit pipes 3 and 4 with the section thereof formed as a circular shape must be connected to change-over mechanism 1 with the section thereof having a square hollow shape at the outlet side of change-over mechanism 1, it is necessary that end surfaces 2', 3' and 4' of the respective main pipe 2, circuit pipe 3 and circuit pipe 4 are made square and hollow at the connecting sides of the pipes to change-over mechanism 1. Accordingly, one end 2" of main pipe 2 is made circular in cross section and the other end surface 2' of main pipe 2 is made square in cross section, one end 3" of circuit pipe 3 is made circular in cross section and the other end surface 3' of circuit pipe 3 is made square in cross section and also one end 4" is made circular and the other end surface 4' is made square. This means that all the pipes should have their other end surfaces made square as well as their one end made circular, all in cross section. This special configuration raises the the cost of manufacturing the pipes and a relatively large space is needed to accommodate the pipes including the change-over mechanism. According to the mechanism of the example stated above, some faults were recognized in that the fluid as the transporting media (such as air or liquid) is liable to be short-circuited under a pressurized transportation to decrease the transporting efficiency.